Lab#3: Heat of Fusion of Ice

Name ______Date ______Per ______

Lab#3: Heat of Fusion of Ice

Introduction

The amount of energy required to convert a solid to a liquid, at constant pressure and temperature, is called the heat of fusion of the substance. It is often convenient to speak of the molar heat of fusion. The molar heat of fusion is the amount of energy required to completely change one mole of a solid, at its melting point, into a liquid.

In this experiment, the molar heat of fusion of ice will be determined. The equation for

the change of state involved is as follows:

1 mol H2O (s) + molar heat of fusion —> 1 mol H2O (l)

The ice will be melted by placing it in a known volume of hot water contained in a plastic foam cup (a calorimeter). The system will be left undisturbed until all the ice has melted. The heat lost by the water will be absorbed by the melting ice. The volume of the ice that melts can be determined by measuring the volume of the water in the cup before the ice is added and after the ice has melted. If the mass of the ice melted and the heat absorbed by the ice are known, the heat required to melt one mole of ice can be calculated.

Objective

In this experiment, you will determine the molar heat of fusion of ice using a calorimeter.

Equipment

(1) Styrofoam cup 1 ring stand

(1) 100-mL graduated cylinder 1 iron ring

(1) 250-mL beaker 1 wire gauze

(1) 400-mL beaker 1 thermometer

(1) hot plate

(1) spatula

Procedure

1. Add approximately 100 mL of tap water to a 250-mL beaker, and heat the water to 60oC, using a gas burner and standard ring stand assembly. While the water is heating, fill the Styrofoam cup halfway with ice cubes. Place the cup in a 400-mL beaker for support.

1. When the temperature of the water has reached 60oC, use two 20-mL portions of this hot water to preheat a 100-mL graduated cylinder. Rinse the cylinder with each of the hot water portions and discard the rinses.

1. Pour 30 mL of the hot water into the graduated cylinder. Record the volume of this water to the nearest milliliter. Measure and record the temperature of the water to the nearest 0.1oC.

1. Quickly drain any excess water from the ice cubes in the cup. Add the measured hot water to the ice in the cup. Stir the ice water rapidly, but with care, until its temperature falls to 2oC. At this point, some unmelted ice should remain in the cup. If, in fact, all the ice has melted, add a bit more so that some ice remains unmelted when the temperature is 2oC or below. Record the lowest temperature of the mixture of ice and water.

1. Using the spatula, quickly remove any unmelted ice from the cup. As you remove the ice, drain as much water from your spatula back into the cup.

1. Carefully pour the cold water from the cup into the graduated cylinder and record the final volume to the nearest milliliter.

Data and Analysis

Prepare a table for your data using the following as a guide.

1. Calculate the change in the temperature of the hot water.

1. Calculate the heat lost by the hot water.

1. Calculate the volume of ice melted. Mass? Remember that the density of water is 1g/mL.

1. Calculate the heat of fusion of ice. (J/g)

1. Calculate the percent error in your determination of the value for the molar heat of fusion of ice. Your teacher will give you the accepted value for this quantity.

% error = (|Your Result - Accepted Value| / Accepted Value) x 100

Conclusions (on a separate sheet of paper)

1. Compare your value for the molar heat of fusion with other lab groups. Does the value depend on the volume of water used? Does it depend on the mass of the ice melted? Does it depend on the final temperature of the mixture?
2. In order to do the calculations, you assumed that all the heat lost by the hot water was absorbed by the ice, causing it to melt. Was this assumption correct? Explain.
3. What assumptions were made about the temperature of the ice at the start and finish of their experiment? Would it affect the results it these assumptions were not correct? Explain.
4. A solid substance with a mass of 200g is at its melting point temperature in a calorimeter. While the substance changes from a solid to a liquid at the same temperature, the 400g mass of water in the calorimeter goes from a final temperature of 30oC from an initial temperature of 80oC.

a. How much heat did the water lose while the substance melted?

b. What is the heat of fusion of the substance that melted in the unit of J/g?